1. Field of the Invention
The present invention relates to a four-wheel steering system for automotive vehicles, more particularly to an electric control apparatus for a rear wheel steering mechanism in the four-wheel steering system for controlling a set of dirigible rear road wheels in accordance with a yaw rate of the vehicle.
2. Discussion of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 60-161255 is an electric control apparatus for a rear wheel steering mechanism which includes a yaw rate sensor arranged to detect a yaw rate of the vehicle for conducting steerage of a set of dirigible rear road wheels in proportion to the detected yaw rate. Under control of the control apparatus, however, the rear road wheels are steered in the same direction as the front road wheels in steady-state cornering of the vehicle. This decreases the yaw rate gain, resulting in deterioration of the maneuverability of the vehicle.